May I ask why you're building your own? Or are you customizing a generic box (like a Dell)?
I've priced building my own PC from the box up and it's almost always more expensive to build it yourself than to buy a generic box (i.e., DELL). This is because the high volume manufacturers get deep price breaks on software - Microsoft gives Dell/Gateway/Acer huge discounts on the OS and Office. They also get PAID to put freeware/shareware on your box. I know it's a pain, but every new computer I get I spend probably a couple of hours removing the freeware off the box right after I open the box.
For most photo editing, even a PhotoShop user (it's a resource hog), a generic box will do fine if you add enough RAM. My newest box I even overdid it - 7 processors, 12GB RAM, terrabytes of disk space. I could edit video with this thing many times over and I just don't use the box's capability.

